Steel making method

ABSTRACT

Iron or steel products are produced from oxide ores in a unique process which utilizes air and regular coal as its primary energy source and wherein the ore is melted in a carbon dioxide zone for separation and absorption of the iron oxides into a slag which is transferred to a carbon-monoxide generating zone. In the latter zone the iron oxides are reduced to form the iron or steel product. Carbon monoxide containing flue gas from the latter zone is burned with air and utilized as a heat source in the carbon dioxide zone. Slag from the various unit processes is collected and used to preheat process air by either continuous operation or in a semi-continuous regeneration process. In both modes of slag preheating, flue gas is utilized to maintain the temperature of the slag bath and high temperature air preheating prior to the slag bath. The molten metal is refined by atomizing in slag or protective gas and may be formed into a sheet by extrusion through a slot-shaped orifice into a space defined between two perforated plates, with a protective gas injected through the perforations serving to support the metal sheet as it solidifies and cools. The thermomechanical treatment of the metal may be carried out by the simultaneous cooling and rolling in a protective atmosphere.

BACKGROUND OF THE INVENTION

Drastic increases in the cost of petroleum fuels and electrical energyhave forced many energy intensive industries, including themetallurgical industry, to adapt to alternate sources of energy, i.e.regular coal, and to search for means of energy conservation. Many ofthe metallurgical processes in current use require energy intensiveancillary processes for coke production, pellet production, oxygenproduction, etc. In most of these conventional processes the sensibleheat of the molten metal and waste slag is simply lost. The prior artbatch and semi-continuous processes which require transfer of the metalmelt from one furnace to another or to and from a ladle all evolve asubstantial amount of pollutants and heat into the atmosphere duringeach transfer and are to that extent thermally inefficient and a sourceof pollution. Further, the low rate of metal processing in comparison tothe high volume of gases which characterizes the conventional processes,requires high surface area of furnace per ton of metal produced andresults in correspondingly high heat losses.

Accordingly, it is an object of the present invention to provide aprocess of high thermal efficiency and low energy consumption for theproduction of steel and steel products (cast, sheets, strips, powder,etc.) from the iron ore, scrap, etc.

It is another object of the invention to provide a thermally efficientprocess in which regular coal may be used as the only or primary sourceof energy.

Yet another object is to integrate the various smelting, refining,solidification and shaping steps involved in the manufacture of steelproducts into a single continuous process wherein the various unitprocesses are conducted in sealed vessels connected in series.

Yet another object of this invention is total utilization of the channelenergy of coal in metallurgical processes.

Still another object is to provide techniques whereby the sensible heatof flue gases, molten metal, and waste slag can be recovered andrecycled within a metallurgical process.

Still another object of the present invention is to provide a processfulfilling the foregoing objectives with minimum atmospheric pollutionand heat losses.

Still another object of the invention is the improvement of metalquality by deep refining, controlled solidification, thermal-mechanicaltreatment and surface protection.

These and other objects and features of the present invention willbecome apparent from the detailed description to follow, taken inconjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

In accordance with the present invention a thermodynamically optimizedheat balance is provided in an integrated process for producing steelproducts from iron ore and coal (and optionally scrap) in which regularcoal may be used as the sole or principal source of energy. The overallprocess is extremely thermally efficient due to utilization of heat frommolten waste slag, heat from the flue gas, and heat liberated by themolten metal during solidification, termination of ancillary operationsand reduction of heat losses.

In one aspect, the present invention provides for the separation ofmelting and reduction. This enables smelting in an oxidizing atmosphereand total utilization of the chemical energy of carbon monoxide producedin a smelting zone, as well as extraction of readily oxidized impuritiesprior to reduction.

The present invention provides for melting fluxing agents and the ironoxide ore together in a first zone to form a molten slag. The ironoxides are selectively absorbed into the slag thereby producing adensified slag. The slag in the first zone tends to stratify with thedenser, iron oxide-rich slag collecting at the bottom of the zone. Theiron oxide-rich slag phase is transferred from the bottom of the firstzone to a second zone wherein coal is injected into the molten slag toreduce the iron oxides and liberate the metal product which separates asa separate lower phase. Flue gas from the second zone containing carbonmonoxide is injected into the slag in the first zone along with anadditional amount of air for combustion of the carbon monoxide, whichcombustion serves as a source of heat for operation of the first ormelting zone.

The first (melting) zone and the second (reducing) zone may beestablished in separate furnaces with the first zone positionedvertically above the second zone to facilitate transfer of the ironoxide-rich slag from the first zone to the second zone. The second zonecontains pools of ferrous metal and slag. The slag from the first zonecan be fed into the slag of the second zone and reduced by the coalsupplied into this slag or the slag from the first zone can be fed intothe metal body and reduced by the carbon dissolved in the metal phase.

Alternatively, a single unitary body of molten slag may be divided intoa lower second zone and an upper first zone by appropriate distributionof air jets, and of coal and ore injection points around the slag body.In this latter embodiment the body of melt is cylindrical in shape andair jets arranged around the upper circumference of the reactor create aflow pattern of molten slag which moves radially toward the center ofthe body of molten slag. As the molten slag moves radially through thefirst (melting) zone it becomes densified by release of gas into thespace in the reactor above the melt surface. The densified slag willsink, i.e. circulate, downwardly through the center of the lower secondzone carrying with it the absorbed iron oxides. Coal and air, in astoichiometric ratio where combustion results in the generation ofcarbon monoxide, are introduced at the periphery of the lower portion ofthe melt body, whereby an annular reducing zone is formed around thecentral downwardly moving slag flow. The carbon monoxide generatedwithin the reducing zone and residual air components carry the slagupwardly toward the second zone where carbon monoxide is oxidizing tocarbon dioxide. The major portion of the coal is injected into thesecond zone; however, a minor portion of the coal may also be injectedinto the first zone as necessary to provide sufficient heat for ore andflux melting.

Another key aspect of the present invention is the collection of moltenwaste slag and its use to preheat process air, for example, the processair to zones 1 and 2 mentioned above. Incoming process air is dispersedinto and passed through the collected waste slag, in direct contacttherewith, whereby the incoming air is preheated to a temperatureapproaching that of the collected waste slag. In one suggested mode ofoperation the collected molten waste slag is divided into first andsecond heat exchange sections with continuous circulation of the moltenslag between the two sections. Flue gas from one or more of the processfurnaces is passed through the molten slag in the first section tocontinuously heat the slag pool while the process air is being passedthrough the molten slag in the other section to preheat the air. In thismode of operation the air may be preheated in two stages utilizing afirst stage air preheater wherein the flue gas exiting a section of thewaste slag pool is used as a heat source to preheat the process airbefore its entry into the other section of the slag pool. Excess wasteslag from the pool may be contacted with water to form a granulatedsolid slag construction material and steam. If desired, the steam soproduced and flue gas exiting the first stage preheater may be passed ina heat exchange relationship through another heat exchanger to superheatsteam. In a second suggested mode of operation a continuous supply ofpreheated air to the process is provided for by a plurality of airpreheat units operated cyclically and arranged in parallel with one ormore units serving to preheat the incoming process air while other unitsare being regenerated by hot flue gas exiting the process. In thislatter mode of operation each air preheat unit is in the form of a poolof collected molten waste slag paired with a heat regenerator. In onecycle flue gas is passed, in succession, through the slag pool and thenthrough the heat regenerator of a given unit and, in the next cycle forthat unit the incoming process of air is passed, in succession, throughthe heat regenerator and then the slag pool. These cycles are repeatedin succession so that the temperature of the air exiting the slag poolis maintained within a predetermined range. High temperature airpreheating enables operation with use of little or no oxygen andelectricity in the process by utilization of the heat content of wasteproducts.

In another aspect of the present invention a steel jet entering a vesselfor degasification is saturated with argon at a pressure higher thanargon pressure in the vessel. This results in the atomization of themetal jet as it enters the degasification vessel.

Yet another aspect of the present invention relates to the formation ofmetal sheet from a metal melt by forcing metal melt through aslot-shaped orifice into a space defined between two parallel plates. Inone embodiment the plates are arranged generally in the horizontal andat least the lower plate is provided with a plurality of aperatures forinjection of an inert gas to form a gas pillow to cool, solidify andsupport the formed metal sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a flow diagram of one preferred embodiment of the presentinvention;

FIG. 1A is a schematic illustration showing one arrangement for furnaces1 and 2 of the embodiment of FIG. 1;

FIG. 2 is a flow diagram of a preferred embodiment for air preheat;

FIG. 3 is a schematic illustration of another embodiment for airpreheat;

FIGS. 4A and 4B schematically illustrate an embodiment of the presentinvention wherein two reaction zones are combined and established in asingle furnace;

FIG. 5 is flow diagram illustrating the utilization and recovery of heatgiven up by molten metal upon solidification;

FIG. 6 is a schematic illustration of one embodiment for forming metalsheet;

FIG. 7 is a schematic illustration of an alternative sheet-formingembodiment;

FIG. 8 is a schematic illustration of another embodiment for metalsheet-forming;

FIG. 9 is a schematic illustration of yet another embodiment forsheet-formation; and

FIG. 10 is a schematic illustration of another embodiment forsheet-formation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

One preferred embodiment of the present invention is shown in FIG. 1which diagrammatically illustrates an integrated steel plant. Theintegrated process depicted in FIG. 1 utilizes sealed, pressurizedfurnaces linked in series. As shown in FIG. 1, preheated air, coal, fluxand ore concentrate are introduced into melting furnace 1 through aplurality of side tuyeres. Within melting furnace 1 the ore and flux areabsorbed by a melt at 1300°-1600° C. The heat of smelting is deliveredby the injection of the preheated air, off-gas from downstream reactors,and by the combustion of coal. Iron values from the ore are absorbedinto the resultant slag layer as iron oxides and the iron-rich slagphase settles toward the bottom of reactor 1 from which it iscontinuously removed through a bottom orifices and transferred toreduction furnace 2. Slag of low iron content is continuously removedfrom the upper portion of the slag layer and transferred to the slagpath in heat exchanger 12 to be described in more detail later. Jets ofair and off-gases ensure intensive mixing of the melt in this furnace.

The crushed iron ore concentrate and fluxing agent added into the slagmelt formed in reactor 1 are most conveniently injected with the blastof preheated air. Conventional fluxing materials such as limestone,dolomite, fluorspar, etc. are employed. If additional heat is requiredto maintain the slag melt at 1300°-1600° C., a suitable quantity ofpowdered coal is also injected with the air. A high ratio of air to coalensures complete combustion to carbon dioxide so that little reductionof the absorbed iron oxides will occur in reactor 1.

The air to furnace 1 is supplied by a compressor (not shown) and ispreheated to about 1200°-1500° C. by bubbling through the slag poolcollected in heat exchanger 12. The slag pool in heat exchanger 12 iscontinuously fed by slag 19 withdrawn from furnace 1 and additional slagwithdrawn from reactors 2, 3, 4 and 5, yet to be described. As will bedescribed in more detail in conjunctin with FIG. 2, vessel 12 ispreferably divided into two separate chambers or units with the slagcirculating between them. With such a preferred arrangement flue gasfrom header 23 may be used to heat the slag in one unit or chamber,while process air is preheated in the other.

In reduction furnace 2, the iron oxides contained in the iron-rich slagphase received from furnace 1 are reduced in accordance with reactionssimilar to those occuring in conventional steel making furnaces.

    3Fe.sub.2 O.sub.3 +C→2Fe.sub.3 O.sub.4 +CO

    Fe.sub.3 O.sub.4 +C→3FeO+CO

    FeO+C→Fe+CO

to a small degree carbon monoxide is also oxidized:

    3Fe.sub.2 O.sub.3 +CO→2Fe.sub.2 O.sub.4 +CO.sub.2

    Fe.sub.3 O.sub.4 +CO→3FeO+CO.sub.2

    FeO+CO→Fe+CO.sub.2

As the iron oxides are reduced, droplets of iron form in the slag layerand separate by gravity to form a lower metal layer within the furnace2. Crushed coal and flux are mechanically injected or pneumaticallyinjected with preheated air through a plurality of tuyeres verticallyspaced along the height of the melt. By distributing the feeds in thismanner the rate of raw material absorption and rate of reduction may becontrolled. The air jets in combination with the rising bubbles of COserve to thoroughly agitate the contents of the furnace. Air injectedthrough jets into the upper portion of the slag layer and, optionally,through additional jets above the slag surface provide for combustion ofCO and C for heat to support the reduction of the iron oxides.

It is possible to inject the slag from the first zone into the ferrousmetal in the lower part of the second zone whereby the iron oxidescarried by the injected slag are reduced by the carbon in the metalphase. A constant concentration of carbon in the ferrous metal issustained by the continuous dissolving of carbon from coal supplied tothe metal phase.

The ratio between mass flow rate of slag supplied to the second zone andmass of melt within the reaction determines whether the furnace operatesin a "semi-batch mode" (at low values of this ratio) or in a continuousflow mode (at high ratios). Furnace 2 is operated at an elevatedpressure, i.e., 1-20 atm, to control foaming, to facilitate requiredrate of gas evolving at and to facilitate transfer of the melts to otherfurnaces. As previously noted, the off-gas from furnace 2 is collectedin the off-gas heater 23 and is used as a heat source for furnace 1.

The pressure in reduction furnace 2 is higher than that in ore meltingfurnace 1 to allow for flow of flue gas to melting furnace 1. Flow ofiron-rich slag from furnace 1 to furnace 2 may be provided for byinstallation of furnace 1 on a level above that of furnace 2 asillustrated in FIG. 1A.

By dividing the conversion of ore to iron into separate unit processes,a number of significant advantages are obtained. Firstly, combustion ofCO is the main source of heat, yet operation of furnace 2 under reducingconditions requires a high ratio of CO/CO₂. By burning coal to CO₂ infurnace 1 the full value of the coal burned in furnace 1 may becompletely utilized without interfering with the iron oxide reduction.Secondly, this separation of operations allows furnace 1 to be operatedat a temperature substantially lower, e.g. about 50°-200° C. lower, thanthat of furnace 2 and reduces in size the mass of material which must betreated at the higher temperature. Thirdly, a greater amount ofimpurities can be separated from the metal than in conventionalprocesses wherein ore smelting and reduction operations are performedsimultaneously in the same furnace. This improvement takes into accountthe fact that some impurities are best absorbed into slag and separatedin an oxidizing atmosphere, whereas others are best absorbed andseparated in a reducing atmosphere. Operation in accordance with thispreferred embodiment allows for efficient separation of both types ofimpurities. Fourthly, the load on reactor 3 is substantially reduced.For example, separation of SiO₂ from iron oxides in furnace 1 eliminatesthe need for oxidation of Si in reactor 3.

One economy realized by practice of the preferred embodiment of thepresent invention is in the use of air rather than oxygen for combustionin furnace 2. With the temperature of air preheating at about 1600° K.and temperature of the flue gases at about 1900° K., the air basedcarbon combustion has the same thermal efficiency that oxygen basedcombustion. Therefore air preheating to a temperature of 1200°-1500° C.enables replacement of oxygen by air in the high-temperature technologywith improvement in thermal efficiency. Use of side tuyeres of properdiameter and angle in inclination is also believed to be and improvementover the use of an oxygen lance which enters from the top, whichimprovement along with preheating enables the substitution of air foroxygen without deleterious effect on the thermodynamic and kineticconditions within furnace 2.

The molten iron "semiproduct" which collects in the bottom of reactor 2will typically contain about 0.3-1.0% carbon, as well as someimpurities, e.g. sulfur, phosphorus, which were not removed in the firstand second zones. This "semiproduct" is transferred to reactor 3 whereit is tested with oxygen in what is essentially a conventional techniquefor the conversion of pig iron into steel. In reactor 3 the metal"semiproduct", under a protective flux, is blasted with pure oxygen at acontrolled flow rate to decarburize the metal down to the desired carboncontent, on the order of 0.25%. In addition to decarburization, theoxygen serves to oxidize impurities, such as silicon, phosphorus andmanganese, which are thus extracted from the molten metal and areabsorbed, at least in part, in the slag. The iron "semiproduct" iscontinuously fed from above into the melt which should be intensivelyagitated, for example in the manner taught by U.S. Pat. No. 4,052,197issued to Brotzman, et al. Slag forming agents, desulfurizing agents andcooling agents may be injected directly into the metal bath. Because thereactions between oxygen and various impurities contained in the ironmelt are highly exothermic, conventional practice calls for addition ofvarious cooling agents such as scrap iron, iron oxides, etc. Iron oxidesinjected into the melt serve the dual purpose of accelearting oxidationand cooling. The principal slag-forming agent used in this step islimestone which itself cools the melt by endothermic decompositionyielding CO₂ which serves to further agitate the melt. The resultantlime forms a basic slag cover which serves to absorb SiO₂, MnO₂ andother oxides liberated from the melt.

The oxygen in the reactor 3 may be replaced by iron ore. The necessaryheat can be delivered to the reactor by supplying air and coal to theslag layer.

The mode of operation of reactor 3 determines the final composition ofthe steel product. In the preferred embodiment shown in FIG. 1 reactor 3is operated as a decarburizer with cooling agents added to control thehighly exothermic reaction. However, if desired, reactor 3 can also beoperated as a carburizer with heating, e.g. by electrical induction orcoal combustion. Various alloying elements may also be introduced intoreactor 3.

The steel product formed in reactor 3 is continuously drawn off from themetal melt and transferred to holding chamber 4 where the temperatureand composition of the metal are allowed to average and gases and slagcomponents are allowed to separate and are drawn off.

If further refining is required, the molten steel is drawn from holdingchamber 4 and is injected as a jet of atomized metal into a slag melt inreactor 5. The conventional electro-slag refining process (ESR) hasdemonstrated that atomization in slag provides a very large metalsurface area for reaction and allows refining to a high degree ofpurity. In the process of the present invention the need for electricalenergy is eliminated because the metal fed to reactor 5 is molten.Moreover, a higher degree of atomization is achieved. In the presentprocess metal atomization is in part the result of the oxidation ofcarbon within the metal phase and an additional increment of atomizationis achieved by a pressure differential between hold tank 4 and reactor5, on the order of up to 1 atmosphere. When metal entering reactor 5 isdepressurized the equilibrium of CO dissolved within the metal phase isshifted and CO is liberated to provide the additional increment ofatomization. Treatment in reactor 5 provides for a further reduction ofimpurities, notably sulfur and phosphorus.

The refined metal from reactor 5 is next stripped of residual gases bytreatment with an inert gas. A metal stream entering reactor 6 isimpinged by a jet of a protective gas such as argon. Argon gas isinjected into the nozzle through which the metal melt is introduced intoreactor 6 and is initially dispersed therein as a discontinuous phase.As the metal stream enters the interior of reactor 6, and drops throughthe argon atmosphere contained therein, a drastic pressure reductionresults and a phase inversion occurs in which the metal stream is againatomized. Degasification here is similar to that in vacuum meltingprocess. The degassed steel melt collects in the bottom of reactor 6 andis continuously transferred to a vessel 7 where the melt is held at1520°-1550° C. for subsequent feed to solidification and shapingoperations. Although the composition of the end-product is generally setin reactor 3, if desired, additives can be introduced into vessel 7 forthe purpose of further adjusting the composition of the steel product.

The refined steel product produced as described above may then besolidified and shaped in any conventional manner, e.g. by continuouscasting or pouring in molds. However, the present invention provides amore effective means of solidification and forming which enables controlof the metal properties and recovery of the heat content of the moltenmetal. For example, in unit 8 (as will be described in more detail inconnection with FIG. 6) steel sheet may be formed by continuouslyremoving the liquid metal from a slot-shaped orifice provided at thebottom of holding vessel 7 and supporting the liquid metal stream on aninert gas, e.g. argon gas, blanket formed by impinging the liquid metalstream with a plurality of argon jets. The metal sheet forms a"hydrofoil" as it slides over the argon pillow and at the same time isimpinged from above by argon jets to protect the sheet againstcontamination and to provide the desired rate of cooling. A high heatexchange co-efficient exists between the argon gas jets and the steelstrip and, as a consequence, a high rate of solidification is achieved.The solidification in the liquid layer, flowing between two extremelyturbulent gas pillows, enables control of the thickness of the layer aswell as the rate of cooling and results in metal properties similar toor better than those obtained in in ESR or vacuum melting, without,however, high energy consumption. The sheet formed on an argon blanketin unit 8 may then be passed through rolling mill 9 and a cooler 10 toprovide a sheet product.

Another technique for producing metal sheet of the required thickness isby pouring an additional portion of a melt of the same or another metalonto the upper surface of a solid metal sheet, creating a thin liquidlayer with rapid solidification of this layer by argon jets. In such away the required thickness of an end product may be achieved bycontrolled homogeneous solidification of consecutively applied thinlayers.

As previously mentioned a key feature of the present invention, and ofthe energy economies which it embodies, resides in the utilization ofslag at 1300°-1600° C. as a heat source. A preferred embodiment for theutilization of waste slag as a heat source will now be described ingreater detail with reference to FIG. 2. FIG. 2 shows the molten slagheat exchanger divided into two units or chambers 12A and 12B. Themolten slag in 12B is less saturated with gas and therefore more densethan the molten slag in 12A and, accordingly, will flow from 12B to 12Athrough the lower conduit. The rate of continuous recirculation betweenthe two units or chambers 12A and 12B through conduits 52 may becontrolled by regulation of gas flow rates, by maintaining adifferential in the respective levels of the molten slag and/or bypositioning the various slag inlets and outlets for conduits 52 toprovide for static head differentials. Typically the upper conduit 52will enter 12B above the level of molten slag. As is further shown inFIG. 2 the ambient air is preheated in two stages. In the first stagecompressed ambient air (from a compressor not shown) is heated in heatrecuperator 11, a conventional dual-path ceramic brick heat exchanger,by heat exchange with flue gas exiting the molten slag heat exchanger12A. The heated air exiting recuperator 11 (first stage air preheater)is further heated by direct contact with molten slag in 12B wherein itis injected into the bottom of the vessel through a plurality of portsor gas dispersion means. Molten slag heat exchanger 12B operates in acounter-current fashion with the air bubbling upward through the moltenslag and the molten slag circulating from top to bottom. The molten slagcontained in vessel 12A is continuously heated by direct contact withthe flue gas collected in header 23 from the various process furnaces.The flue gas is dispersed and bubbled through the molten slag in 12A andthen sent to heat recuperator 11 as previously described. If additionalheating of vessel 12B is required, coal may be injected with theincoming air. Likewise, coal and air may be injected into vessel 12A.Slag over-flow from 12A is injected into vessel 14 wherein it is cooledand granulated by a water spray which is thereby converted to steam. Thesolidified granular slag product removed from the bottom of vessel 14may be used as a construction material. Steam from 14 is further heatedin conventional tubular heat exchanger 13 by counter-current heatexchange with flue gas exiting heat exchanger 11.

An alternative system for utilizing the heat of molten slag to preheatprocess air is shown in FIG. 3. FIG. 3 shows a heat regenerator 80linked in series with vessel 82 holding a bath of molten slag 19.Regenerator 80 is a conventional heat exchanger, similar to heatrecuperator 11 of FIG. 2, but having a single gas flow path defined bythe ceramic bricks contained therein. These vessels operate cyclicallyin parallel with pairs of like vessels to provide a continuous flow ofpreheated air to furnace 1. In the cycle shown in FIG. 3, flue gas 23 ispassed, successively, through the slag bath in vessel 82 and thenthrough regenerator 80. Upon the regenerator 80 reaching a predeterminedtemperature the positions of valves 51a, 51b, 51c and 51d are switched,the flow of flue gas through the units discontinued and process airpassed, successively, through regenerator 80 and slag heater 82. Uponthe temperature of regenerator 80 falling below a predetermined valuethe positions of valves 51 are again reversed and the cycle is repeated.

FIGS. 4A and 4B depict an embodiment wherein the ore melting function offurnace 1 and the ore reduction of furnace 2, as depicted in FIG. 1, arecombined in a single reactor 2A. Preheated air is injected into theupper portion of reactor 2A at a plurality of points around itscircumference to create melt flow zone 37. The air injected into zone 37oxidizes the carbon, carbon monoxide and slag elements as they enterzone 37 from peripheral zone 39 below. The major portion of the coal tofurnace 2A is injected into the lower portion of the slag in zone 39 andreacts to form carbon monoxide and to reduce iron oxides absorbed intothe slag in zone 37 and received through zone 38. Upward flow throughreducing zone 39 is induced by the gases injected thereon (e.g. nitrogencomponent of air) and generated therein, resulting in circulation ofslag within the slag layer as depicted by arrows 36. With reference toFIG. 4B, the rising gases cause flux to flow upward through reducingzone 39 into melting (oxidizing) zone 37 where, upon reaching the uppersurface of zone 37, the gas is released and the densified slag thencirculates downward through zone 38. Carbon monoxide which is generatedin zone 39 is converted to carbon dioxide as it comes into contact withair entering through jet 34 resulting in the generation of an additionalincrement of heat in carbon dioxide zone 37. Ore, flux and, optionally,a minor portion of the coal are injected into the slag at points inclose proximity to air jet or jets 34. These additives are carried bythe air jet and melted in carbon dioxide zone 37A. Because carbonmonoxide generated within 39 is oxidized to carbon dioxide as it enterszone 37, zone 37 operates as a melting zone with little reduction ofiron oxides in a manner analogous to the operation of furnace 1 in theembodiment of FIG. 1. Slag containing the iron oxides absorbed from theore travels downwardly through zone 38 and enters carbon monoxide zone39 wherein it is reduced as in the operation of furnace 2 in theembodiment of FIG. 1. An additional air jet(s) 35 may be provided in thegas space above the molten slag to oxidize any residual carbon monoxide.It can be appreciated from the foregoing that the molten slag in reactor2A is thoroughly mixed, i.e. by the gas generated, by the reactantsinjected into the slag, by the difference in density between the slagsin zones 38 and 39 and by the air jets.

Yet another energy economy included in the preferred embodiment is thatwhereby the heat given up by the molten metal during gas refining in thereactor 6 and the sheet forming and cooling processes is recovered assensible heat from the argon gas exiting degaser 6 and sheet former 8.As illustrated in FIG. 5 a compressor 16 is driven by a turbine jet 15which, in turn, is driven by the hot argon which exits units 6 and 8 ata pressure of approximately 1-2 atmospheres. Thus the hot argon gasdrives turbine jet 15 which optionally produces electricity and in turndrives compressor 16 and serves to compress the argon exiting turbine 15by operation in a Brayton cycle.* The overall thermal efficiency of thecycle depends on the energy losses in supply lines and nozzles. Highpressure, cooled argon exiting compressor 16 may optionally be cleanedin a gas purifier 42 prior to recycle to degaser 6 and sheet former 8.

Metal solidification and sheet forming by an argon pillow or "hydrofoil"technique, as incorporated into the embodiment previously described inconnection with FIG. 1, is shown schematically, in more detail, in FIG.6. As shown in FIG. 6 liquid metal is forced out of the slot-shapedorifice at the bottom of holding vessel 7 at a rate proportional to thetotal of the static head and gas pressure within vessel 7. Initially,the molten metal flows over a thin support strip 70 made of ceramic,asbestos, or metal. The metal melt solidifies as it passes through a gapbetween upper and lower horizontal, aperatured plates 72 and 74. Argonat a pressure of 1.5-20 atmospheres in high pressure header 50 passesthrough the apertures as an array of jets to create a frictionlesssupport pillow for the moving metal strip. A protective gas (argon)blanket is simultaneously applied to the top of the solidifying stripfrom a low pressure header 49. The argon exiting these gaps is fed toturbine 15 as previously described in connection with FIG. 5.Experimental investigation has shown that the coefficient of heatexchange between argon jet arrays and hot metal sheet can be 1000 to1500 BTU per square foot hour. The rate of heat extraction from themetal and consequently the rate of cooling and solidification isdetermined by the rate of gas supply and gas flow characteristics in theheader 50. The thermal treatment may be combined with mechanicaltreatment by rolls 9 which may also be operated in a protectiveatmosphere.

Another scheme for sheet formation is shown in FIG. 7, wherein the sameor different molten metal is poured onto presolidified metal at aplurality of points distributed along the travelling sheet. The sheetmay be mechanically worked by rolling between the points where themolten metal is applied.

Alternative schemes for metal solidification and production of steelsheet or slab are shown in FIGS. 8, 9 and 10. In the embodiment depictedin FIG. 8 units 6, 7 and 8 of the previously described embodiment areeliminated and steel sheet or slab is produced directly from the meltaccumulated at the bottom of slag refiner 5 by means of rolling mill 60.In the embodiment depicted in FIG. 9, operation of degasser 6,previously described, is modified for operation as a fluidized bed withthe temperatures of the incoming metal and argon gas regulated so thatthe droplets of atomized and fluidized metal are cooled to a temperatureapproaching the temperature of solidification when collected at thebottom of the vessel 6. Degassification and atomization is provided forby argon injection in a manner previously described. Additionally,fluidization is provided for by injection of argon through a pluralityof points at the bottom of the vessel as indicated by the arrows. Again,steel sheet or slab 43 is formed by a roll mill 62. The solidificationcan be completed in a gas flow or by quenching in water bath.

Yet another alternative for forming steel sheet employs a modifiedversion of holding vessel 7 as depicted in FIG. 10. In FIG. 9 relativelycool steel strip 64 is fed by feed rolls 66 and rolling mill 68 throughthe bath of liquid metal in holding tank 7. As the cool strip 64 entersthe molten metal bath, steel crystallizes on its surface. Thetemperature of the incoming strip 64 and its residence time within themolten metal bath are regulated to prevent remelting of the surfacedeposit. The steel strip carrying the newly formed steel surface depositis then rolled by mill 68 to form a finished product 43 of the desiredthickness.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed is:
 1. A process for producing ferrous metal productsfrom an ore containing iron oxides, said process comprising:(a) meltingfluxing agents and the iron oxide ore together under oxidizingconditions in a melting furnace to form a molten slag, with littlereduction of the iron oxide ore; (b) allowing said molten slag tostratify whereby iron oxide-rich slag collects at the bottom of saidmelting furnace; (c) transferring said iron oxide-rich slag from thebottom of said melting furnace to a reduction furnace separate from saidmelting furnace; (d) injecting coal and air into said reduction furnaceto form carbon monoxide and to establish reducing conditions within saidreduction furnace, thereby reducing the iron oxides to form a moltenferrous metal product; and (e) injecting into the molten slag withinsaid reducing furnace, below the surface of the slag, (1) the off-gasfrom said reduction furnace containing carbon monoxide and (2) air forcombustion of said carbon monoxide to form carbon dioxide, therebyestablishing said oxidizing conditions within said melting furnace. 2.The process of claim 1 wherein the molten slag in said reducing furnaceis maintained at a temperature at least 50° C. higher than in saidmelting furnace.
 3. The process of claim 1 wherein the molten slag insaid melting furnace is at a higher level than the molten slag in saidreducing furnace to facilitate melt flow to the reducing furnace.
 4. Theprocess of claim 1 wherein said reducing furnace is maintained at anelevated pressure of 1-20 atmospheres, said elevated pressure beinghigher than that in said melting furnace.
 5. The process of claim 1wherein additional quantities of ore are injected into the slag melt insaid melting furnace below the surface of the melt and melted therein.6. The process of claim 5 wherein said additional quantities of ore arepneumatically injected into said melting zone with the air.
 7. Theprocess of claim 1 wherein said air to said melting furnace is preheatedto 1300°-1600° C.
 8. A process for producing ferrous metal products froman ore containing iron oxides, said process comprising:(a) meltingfluxing agents and the iron oxide ore together in a first zone to form amolten slag; (b) allowing said molten slag to stratify whereby ironoxide-rich slag collects at the bottom of said first zone; (c)transferring said iron oxide-rich slag to a second zone; (d) injectingcoal and air into said second zone to form carbon monoxide and to reducethe iron oxides to form a molten ferrous metal product; (e) transferringoff-gas from said second zone containing carbon monoxide to said firstzone and combusting said off-gas with air in said first zone; (f)removing slag from at least one of said first and second zones andcollecting said removed slag as a pool of molten slag; and (g) passingthe air to at least one of said first and second zones through said poolof molten slag to preheat said air.
 9. The process of claim 8 whereinsaid air is preheated to 1300°-1600° C.
 10. The process of claim 8further comprising:dividing said pool of molten slag into first andsecond heat exchange sections and continuously circulating the moltenslag between said first and second heat exchange sections; collectingflue gas from at least one of said first and second zones and passingsaid flue gas through the molten slag in said first section, therebycontinuously heating the slag pool; and passing the air to at least oneof said first and second zones through said molten slag in said secondsection to preheat the air.
 11. A process in accordance with claim 10wherein said air is preheated in two stages, said process furthercomprising:passing said flue gas exiting said first section and said airentering said second section in a heat exchange relationship through afirst-stage air preheater.
 12. A process in accordance with claim 11further comprising:removing molten slag from said pool and contactingthe molten slag from said pool with water to form granulated solid slagand steam; and passing said steam and said flue gas exiting the firststage air preheater, in heat exchange relationship, through a steamsuperheater.
 13. A process in accordance with claim 8 furthercomprising:providing a plurality of parallel molten slag pools and aheat regenerator paired in series with each slag pool; passing a flow offlue gas, in succession, through the slag pool and then the heatregenerator of one pair; discontinuing the flow of flue gas through saidone pair and then passing the air to at least one of said first andsecond zones, in succession, through the heat regenerator and slag poolof said one pair; and successively alternating the flows of flue gas andair through said one pair to maintain the temperature of the air exitingthe slag pool within a predetermined range.
 14. In a metalurgicalprocess for the separation of metal values from a raw material into amolten slag phase utilizing air as a reactant, the improvementcomprising:collecting molten slag from the process into a pool of moltenslag divided into first and second zones; continuously circulating theslag between said first and second zones; passing the air to the processthrough said second zone of said pool to preheat the air; and collectinghot flue gas from the metalurgical process and passing said flue gasthrough the molten slag in said first zone, thereby continuously heatingthe slag pool.
 15. A process in accordance with claim 14 wherein saidair is preheated in two stages, said process further comprising:passingsaid flue gas exiting said first zone and said air entering said secondzone in heat exchange relationship through a first stage air preheater.16. A process in accordance with claim 15 further comprising:removingmolten slag from said pool and contacting the molten slag from said poolwith water to form granulated solid slag and steam; and passing saidsteam and said flue gas exiting the first stage preheater, in heatexchange relationship, through a steam superheater.
 17. A process inaccordance with claim 14 further comprising:providing a plurality ofmolten slag pools in parallel and a heat regenerator paired in serieswith each slag pool; passing a flow of flue gas, in succession, throughthe slag pool and then the heat regenerator of one pair; discontinuingthe flow of flue gas through said one pair and then passing the air toat least one of said first and second zones, in succession, through theheat regenerator and slag pool of said one pair; and successivelyalternating the flow of flue gas and air through said one pair tomaintain the temperature of the air exiting the slag pool within apredetermined range.
 18. A process for producing ferrous metal productsfrom an ore containing iron oxides, said process comprising:(a) meltingfluxing agents and the iron oxide ore together in a first zone to form amolten slag; (b) allowing said molten slag to stratify whereby ironoxide-rich slag collects at the bottom of said first zone; (c)transferring sid iron oxide-rich slag to a second zone; (d) injectingcoal and air into said second zone to form carbon monoxide and to reducethe iron oxides to form a molten ferrous metal product; (e) transferringoff-gas from said second zone containing carbon monoxide to said firstzone and combusting said off-gas with air in said first zone; (f)collecting the molten iron or still metal product at the bottom of saidsecond zone and transferring said metal product to a third zone; (g)contacting the molten metal product in said third zone with oxygen orair to reduce the carbon content; (h) holding the metal from said thirdzone in a quiescent fourth zone to allow residual slag and gasimpurities to separate; (i) injecting the molten metal from said fourthzone into a reactive molten slag in a fifth zone for furtherpurification; and (j) atomizing the molten metal from said fifth zone inthe presence of an inert gas to wash out residual dissolved gas.
 19. Aprocess for producing ferrous metal products from an ore containing ironoxides, said process comprising:(a) melting fluxing agents in acylindrical furnace to form a cylindrical body of molten slag, said bodybeing in communication with a gas space above its upper surface; (b)injecting air and coal into a lower portion of said body of molten slagto establish reducing conditions and a reducing zone; and (c) injectingadditional air into an upper portion of said body of molten slag from aplurality of points surrounding the circumference of said body of moltenslag to establish oxidizing conditions and a melting zone, said coalreacting with air in said reducing zone to form carbon monoxide whichcirculates into said melting zone for reaction with said additional air,said air injection into said melting zone creating a flow pattern ofmolten slag moving radially toward the center of said body, saidradially moving molten slag becoming densified as it releases gas intothe gas space above said melting zone, and said densified slagcirculating downwardly through the center of said slag body and intosaid reducing zone.